Single Micro-nano Sphere’ Scattered Field Amplitude And Phase Distribution Research Under A High NA Objective

Optical detection of individual non-luminous micro-nano particle has important research values in biomedical, nanophotonics and other fields. For example early diagnosis of major diseases can be used as molecular probes to achieve molecular level biological target detection at the cellular level. However, using optical methods to detect micro-nano scale particles have a big challenge as the needle in the haystack, because extremely weak signals have been submerged in strong background noise. Our group work designed the orthogonal polarization microscopy imaging system that can achieve the detection of small individual 5nm gold particles in the early research work. In this paper, we use this system to study the amplitude and phase variation of the scattered light field between the light and polymer interaction. We aim to study the direct imaging and size identification method of biological targets without marking in a biological environment in support of the high sensitivity detection imaging system.Polystyrene microspheres have the similar optical properties to the biological environment, which are commonly used in the simulation of biological systems. In this paper, we use them as biological targets, we study:1) the amplitude and phase of the scattered light field distribution when the particle interaction with the high focused beam. We main use the orthogonal polarization and heterodyne interferometry principle to study it, the linearly polarized light in x direction after a high numerical aperture objective become high converging beam, it interact with particle to produce scattered field, then the collection objective collects the scattered field and mix with y polarization reference light, so we obtain the y direction scattering field amplitude and phase distribution of particles; 2) based on the particles’ scattering filed amplitude and phase distribution characteristics images to determine particle size method. We used Mie scattering and FDTD algorithm to set simulation models. Based on the simulation results we analyzed and compared the particles scattering field amplitude and phase image distribution characteristics have effects on the single micro-nano particle size. Meanwhile we used our group preliminary design the orthogonal polarization microscopic imaging system to make the experimental verification. We determined a method to distinguish particles size by its amplitude and phase distribution pattern; 3) the depolarization contribution for the focused beam of different particles with 50nm～1μm diameter. We mainly calculated the relative depolarization conversion rate values between the different diameter single micro-nano particles and focused beam.In this paper, we achieved unmarked detection and sized method of the diameter distribution in 50nm～1μm polymer micro-nano spheres by comparing the numerical simulation results and experimental data. Innovation of this paper is as follows:1) we further analyzed focused field’s Mie scattering under the high numerical aperture lens. With the particle diameter increases, the amplitude image distribution characteristics changed from four flap structure into shell structure and in the center position of the particle the phase distribution changed from essentially unchanged, slowly changing to rapidly changing; 2) we determined a method to distinguish particles size by its amplitude and phase distribution pattern. When the particle amplitude distribution pattern is the four flower structure and phase distribution in the particle center position is almost the same, the particles size are generally less than 200nm; when the particle amplitude distribution pattern is weak shell-like structure, and there is a slow phase change in the particle center position, particles size are generally less than 600nm; when the particles amplitude distribution pattern is obvious shell-like structure, and there is a clearly phase leap in the particle center position, the particles size generally between 600nm to 1μm; 3) we determined the minimum critical the incident angle 37° under a high numerical aperture objective (NA=1.2) when it produce depolarization effect, and that can be applied to speed up the FDTD simulation efficiency.